The invention relates to a process and an apparatus for producing an aerosol from a pulverulent substance, particularly a medicinal substance.
For the treatment of diseases of the respiratory tracts, medicinal substances are preferably applied by inhalation, because as a result the active substance is deposited in relatively high concentration on the respiratory tracts, whereas effects due to the distribution of the medicinal substance throughout the body, so-called systemic effects, remain relatively limited. In addition, the inhalation of a medicinal substance is also suitable for systemic therapy.
The production of a suitable aerosol with effectively inhalable, i.e. relatively small, particles in part leads to considerable difficulties, particularly when based on a pulverulent substance. Therefore numerous processes and apparatuses have been developed which in different ways attempt to produce such a readily inhalable aerosol.
Despite the numerous possibilities in connection with inhalators the use of propellants, particularly those prejudicial to the environment, must be avoided. DE-A1-40 27 390 discloses a propellant-free inhalator, in which the medicinal substance is received in powder form in a storage container. By means of a dosing device the substance dose is removed prior to the fitting of a mouthpiece, and from there the patient inhales with the aid of active breathing in, the substance being entrained by the air flow formed as a result of breathing in. In order to obtain inhalable particles of the pulverulent substance, there is an air chamber for distributing the substance in the air flow being formed. The particle size in the case of this inhalator is dependent to a significant extent on the intensity and nature of breathing in, so that adequately small particles of the dosed substance cannot be guaranteed in all cases. For use in the known inhalator the medicinal substance, optionally accompanied by the admixing of adjuvants, is compacted to form a pressed article. Using a moving edge or brush powder is removed from the pressed article and is admixed with the breathing air of the patient. The process is not suitable for mass production, because it is not possible to produce with a homogeneous hardness the pressed articles formed from tile medicinal substance and adjuvant.
DE-A-40 27 391 discloses a further propellant-free inhalator with a similar construction. In order to make the breathed in substance quantity reproducible and simultaneously attain inhalable particles, an air volume stored in a cylinder is automatically released in reaction to the breathing in and is led to a nozzle, so that the dosed substance is blown by the active air flow which forms into the throat of the patient. However, in connection with respiration triggering problems are caused by the considerable effort and expenditure necessary for a precise air volume release triggered by respiration.
However, known processes and apparatuses generally suffer from the disadvantage that there is an imprecise aerosol with respect to the particle spectrum and mist density. Fundamentally, on blowing in, there is a whirling up or turbulent agitation of a considerable air quantity, which is much larger than the blown in volume. This air quantity must normally be trapped in a corresponding container if not inhaled by the patient. If it is directly inhaled by the patient, then the intrabronchial deposition differs to a very marked extent, because as a function of the inhalation flow the particle spectrum is greatly modified mainly by impaction.
On blowing in the accelerated air is decelerated by that which is already present. Therefore the kinetic energy striking the aerosol is not high.
If the blown in aerosol volume is intermediately stored in a container, so that the patient always inhales an identical particle spectrum, large volumes are necessary. In the case of dosing aerosols it is often necessary to use as attached devices spacers having a volume of 300 to 800 ml.
Another inhalator with an active air flow is known from WO-A-90/07351. The air flow is made ready by a pressurized gas source, or is produced with the aid of a piston/cylinder arrangement, and is guided in a nozzle arrangement with a varying cross-section, in order to in planned manner increase the flow rate of the air flow. Close to the maximum flow rate in the nozzle arrangement a duct issues into the flow path and constitutes a connection to a storage container for the pulverulent substance. The substance is sucked in by the active air flow and conveyed into a mixing chamber, where a good distribution of the particles is to take place. In connection with this inhalator it must be borne in mind that the preparation of the aerosol takes place completely independently of the inhalation of the patient, and also an active air flow is directed into the respiratory tracts of the patient, so that a good distribution cannot be expected before and during inhalation.